Peroxydicarbonates have the general formula RO--C(O)--O--O--C(O)--OR wherein R is an alkyl group. These compounds are important for use as free radical producing initiators in the polymerization field, and particularly in the polymerization of vinyl monomers. However, the peroxydicarbonates have one serious disadvantage, and that is their inherent instability. They are sensitive both thermally and to heavy shock and some of them are capable of detonating under certain conditions. Accordingly, it is necessary to take precautions during manufacture thereof in order to prevent decomposition from either heat or shock.
In the past, peroxydicarbonates were made by batch processes where large amounts were handled in order to be economical. However, under such circumstances, explosions have occurred in trying to make a pure product. One answer was to use diluents or inert solvents in the process and then sell a dilute product. This did not completely solve the problem since, in many polymerization processes, it is desirable to use the pure, undiluted product.
It was thereafter proposed to produce the peroxydicarbonates continuously. For example, see U.S. Pat. No. 3,377,373, issued Apr. 9, 1968, wherein the patentees react a chlorocarbonic acid ester with hydrogen peroxide and an aqueous alkali metal hydroxide solution in at least two reaction zones. The reaction is thereafter terminated in an after-reaction zone by addition of a halogenated organic solvent. The solvent solution is then isolated by using various settling vessels, or washing vessels. A similar process using solvents is described in U.S. Pat. No. 3,429,910, issued Feb. 25, 1969. However, when using an organic solvent diluted initiator in a polymerization process, problems arise. First, when using an organic solvent, it has a tendency to remain in the polymer being produced, which, in turn, makes drying of the polymer more difficult. Further, due to the flammability of such organic solvents, removal thereof from the polymer is dangerous and costly. Also, the flammability of organic solvents presents a serious safety problem in storage and handling when they are used as carriers for unstable initiators.
The use of solvents in making the initiators decreases the efficiency of processing. Further, for many polymerization processes, pure peroxydicarbonates are desired. Accordingly, it is most desirable to have a continuous, solvent-free process for making peroxydicarbonates which will increase processing efficiency.